It's curious that Microsoft is making this distinction ... a PC and a tablet, given that the Windows 8.1 operating system runs on both.

Now, it's true that Microsoft also has a tablet-only operating system, Windows RT, but RT already comes with a version of Office. That's one of its selling points.

A Microsoft spokesperson explained that the key thing is that it won't be allowed to be installed on two PCs. One of the two devices has to have a touch screen. That means that Microsoft is cool with a Mac and a Surface. Or a Windows PC and a Surface. But not a Windows PC and a MacBook.

Because if this version doesn't work on the iPad, then $70 a year seems steep. You can pick up the Home and Student version of Office 2013 for just over $100 on Amazon these days and never pay for it again.

(Note that the $70 price is just the target. Retailers might charge less.)

Your other options for getting the latest version of Office are: $99 per year for a version that allows you to install it on up to five devices, Macs and PCs. Students can also buy a two-device version that covers four years for $80.